CN115326601B - Dynamic impact test and evaluation method of anchor-net coupling support rock mass - Google Patents

Abstract

The invention provides an anchor net coupling support rock mass dynamic impact test and evaluation method, and relates to the field of rock mechanics. Aiming at the problem that the shock resistance of the conventional anchor rod and anchor net coupled supporting rock mass is inconvenient to obtain, a coupled rock mass sample with the anchor rod and anchor net arranged is subjected to a high-strain-rate impact test, and a corresponding monitoring assembly is configured to monitor the impact test process, so that evaluation indexes of surface strain, crack evolution characteristics, rock mass destruction strength, anchor rod deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics of the rock mass are established, and the rock mass anchoring effect under the dynamic impact condition is evaluated. The method comprises the following specific steps: arranging an anchor net and an anchor rod on a non-impact surface of the cubic rock mass test piece, pre-tightening, spraying speckles on the surface of the test piece, and obtaining a coupling test piece; arranging a monitoring assembly on the coupling test piece, and applying high-strain-rate impact load; acquiring data of the coupling test piece under impact through a monitoring assembly, and collecting rock mass debris; and processing and analyzing the acquired data, and evaluating the anchoring effect according to the indexes.

Description

Dynamic impact test and evaluation method of anchor-net coupling support rock mass

technical field

The invention relates to the field of rock mechanics, in particular to a rock mass dynamic impact test and evaluation method supported by anchor-network coupling.

Background technique

With the continuous increase of the mining depth of coal resources, deep engineering disasters such as rock burst and large deformation of roadway surrounding rocks are increasing, which pose a great threat to the efficient mining of deep resources. Rock burst is a dynamic disaster in which the accumulated elastic deformation energy of the rock mass in the mining face is released suddenly, resulting in strong vibration and severe damage to the rock mass.

Anchor (cable)-net coupling support is an economical and effective support method. The anchor net can convert the point load of the anchor (cable) pre-tightening force into a surface load, expand the effective area of active support, and improve the quality of the surrounding rock. self-supporting capacity, thereby improving the ability of the surrounding rock to resist dynamic disturbance and impact. In order to test the impact resistance performance of bolt and anchor network coupling, a test device that can simulate the violent failure phenomenon and process of supporting rock mass is needed. The existing laboratory testing equipment fixes one end of the anchor rod and directly applies an impact load to the other end of the anchor rod, so that the actual measured impact resistance of the anchor rod includes the energy absorbed by the entire length of the anchor rod when stretched. The results obtained by the test are quite different from the field characteristics of the bolt. The current test equipment cannot truly reflect the interaction between the bolt and the anchor net-surrounding rock, that is, the impact load on the anchor bolt and the anchor net is inconsistent with the actual situation on site, and It cannot directly reflect the reinforcement effect of the bolt-bolt-network coupling body on the surrounding rock under the action of impact load. At the same time, when the rock mass is severely damaged, it is a high-strain rate failure. , the lack of corresponding test methods, it is difficult to obtain the mutual coupling mechanism between the bolt anchor network and the rock mass.

Contents of the invention

The purpose of the present invention is to aim at the defects existing in the prior art, and provide the rock mass dynamic impact test and evaluation method of the anchor net coupling support, by carrying out the high strain rate impact test to the coupled rock mass sample arranged with the bolt anchor net, and Configure corresponding monitoring components to monitor the impact test process, set evaluation indicators to evaluate the processed parameters, and assist in the study of the mechanism of action between the bolt-bolt-network coupling body and the rock mass.

The dynamic impact test and evaluation method of anchor-net coupling supporting rock mass adopts the following scheme:

include:

Arrange anchor nets and bolts on the non-impact surface of the cube rock mass specimen and pre-tighten them, spray speckle on the surface of the specimen to obtain the coupled specimen;

Arrange monitoring components on the coupling test piece, and apply high strain rate impact load;

Obtain the data of the coupling test piece under impact through the monitoring component, and collect rock debris;

Process and analyze the acquired data, and evaluate the anchoring effect according to the indicators;

Among them, the anchoring effect index includes: rock mass surface strain, crack evolution characteristics, rock mass failure strength, bolt deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics.

Further, the anchor rods are arranged at the four corners of the side of the test piece, the four corners of the side are respectively provided with anchor rods penetrating the test piece, and after the anchor net is arranged, a pre-tightening force is applied to the anchor rods.

Further, the anchor net is continuously arranged around the non-impact surface of the test piece, wraps the test piece and avoids the anchor rod, and pressure monitoring elements are installed at both ends of the anchor rod.

Further, the pre-tightening force of the anchor rod on the test piece can be adjusted, and different pre-tightening forces are configured for different samples to obtain impact test data, and the impact resistance capabilities of the samples under different pre-tightening forces are compared and analyzed.

Further, the monitoring component includes a pressure monitoring element, a stress and strain monitoring element, a displacement monitoring element and an image acquisition element; the pressure monitoring element is arranged on the anchor rod, the stress and strain monitoring element is arranged on the coupling test piece, and the displacement monitoring element is arranged on the coupling test piece. The side of the component is used to monitor the displacement of the rock mass, anchor net and bolt, and the image acquisition component acquires images during the impact test.

Further, the correlation calculation is performed on the gray scale of the speckle image before and after the surface deformation of the coupled specimen, the displacement and strain parameters of the specimen are obtained, and the strain distribution on the rock mass surface of the coupled specimen is calculated.

Furthermore, the box dimension method is used for measurement, and square grids of different yardages are used to cover the measured area. The yardage of the grid is given and the number of grids required to cover the image is calculated, and the fractal dimension of rock cracks is obtained by fitting. number to calculate the crack evolution characteristics.

Further, the dynamic pressure sensor arranged on the bolt is used to monitor the pressure versus time curve, and the peak point of the curve is defined as the failure strength of the rock mass; the laser extensometer is used to measure the displacement of the bolt in real time, and the elongation of the bolt is calculated to obtain Anchor deformation.

Further, the energy absorbed by the coupled specimen and the energy absorbed by the unsupported rock mass specimen are calculated separately, and the energy absorption capacity improvement coefficient is equal to the ratio of the total energy absorbed by the coupled specimen to the total energy absorbed by the unsupported rock mass specimen ;

The broken debris of anchor-mesh coupling supporting rock mass is screened according to particle size to obtain multiple groups of debris with different particle sizes, and the ratio of the mass of each group of debris to the total mass is calculated.

Further, the evaluation includes the following steps:

Standardize each evaluation index;

The subjective and objective comprehensive weighting method is used to obtain the weight of each index;

The fuzzy comprehensive evaluation method is used to evaluate the anchorage effect of rock mass.

Compared with prior art, the advantages and positive effects that the present invention has are:

(1) In view of the inconvenient acquisition of the impact resistance performance of the rock mass supported by the coupling of the bolt and anchor net, the high strain rate impact test is carried out on the coupled rock mass sample with the bolt and anchor net, and the corresponding monitoring components are configured. The impact test process is monitored, evaluation indicators are set to evaluate the processed parameters, and the on-site working conditions are simulated to obtain the impact resistance of the coupled samples.

(2) According to the six indexes of rock mass surface strain distribution, crack fractal dimension, rock mass failure strength, bolt axial deformation, energy absorption capacity improvement coefficient, and rock debris distribution characteristics of anchor network coupling support, the "level Analytical method + entropy weight method" subjective and objective comprehensive weighting method to obtain the weight of each index, use the fuzzy comprehensive evaluation method to evaluate the rock mass anchoring effect, and assist in the study of the mechanism of action between the bolt bolt network coupling body and the rock mass.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention.

Fig. 1 is a flow chart of the rock mass dynamic impact test and evaluation method of anchor-net coupling support rock mass in Example 1 of the present invention.

Fig. 2 is a schematic diagram of the impact test equipment for anchor-net coupling supporting rock mass in Example 1 of the present invention.

Fig. 3 is a schematic diagram of a rock mass specimen supported by anchor-net coupling in Example 1 of the present invention.

Fig. 4 is a schematic diagram of a hierarchical structure model for evaluating the anchoring effect of rock mass coupled with anchor nets in Example 1 of the present invention.

In the figure, 1 Hopkinson dynamic loading system; 2 bullet; 3 laser velocimeter; 4 incident rod; 5 protective cover; 6 camera; 7 coupling specimen; 8 transmission rod; 9 laser extensometer; 10 strain gauge; 12 lock; 13 dynamic pressure sensor; 14 bolt; 15 impact surface of rock mass specimen; 16 rock mass specimen; 17 anchor net.

Detailed ways

Example 1

In a typical embodiment of the present invention, as shown in Fig. 1-Fig. 4, a dynamic impact test and evaluation method of rock mass coupled with anchor net is provided.

Step 1: Prepare a cubic rock mass test piece 16 according to the rock mass dynamics test standard, drill the rock mass test piece 16, drill the hole vertically to the rock surface and penetrate the test piece, and then introduce the anchor rod 14 into the borehole and anchoring agent. After the anchoring agent is solidified, the anchor net 17 is laid, and the tray 11, the lock 12, and the dynamic pressure sensor 13 are installed in sequence, and the pre-tightening force is applied, and the speckle is sprayed on the surface of the rock mass to complete the coupling of the anchor rod 14 and the anchor net 17 to support the rock. The coupled specimen 7 was obtained after body.

Step 2: Arrange the coupling test piece 7 in the Hopkinson dynamic loading system 1, set the protective cover 5, clamp the coupling test piece 7 between the incident rod 4 and the transmission rod 8, and paste the strain on the incident rod 4 and the transmission rod 8 Gauge 10, connect the strain gauge 10 with the ultra-dynamic strain gauge, and start the impact test after the instrument debugging is completed.

Step 3: Place a laser velocimeter 3 between the Hopkinson pressure bar and the impact bar to measure the velocity of the bullet 2 .

Step 4: High-pressure gas is used as the impact power source, the launch tube is embedded in the exhaust port of the compressed air chamber, the bullet 2 is built in the launch tube, and the high-pressure gas is released to drive the bullet 2 to act on the injection rod 4, and the injection rod 4 acts on the rock mass test The component impact surface 15 completes the dynamic impact loading.

Step 5: Use the monitoring system to record the stress, strain, displacement and other data of the coupling test piece 7 under the dynamic impact condition. After the test is completed, the rock mass debris is collected.

Step 6: Evaluate the anchoring effect of the rock mass based on the rock mass surface strain, crack evolution characteristics, rock mass failure strength, anchor rod 14 deformation, energy absorption capacity improvement coefficient and rock mass debris distribution characteristics.

As shown in Figure 1 and Figure 3, the rock mass test piece 16 in step 1 is drilled, and the diameter of the drill hole is slightly larger than the material diameter of the anchor rod 14, so as to ensure that the anchor rod 14 and the tray 11 can be installed reasonably, and the four drill holes are square. Layout to ensure that the anchor net 17 material is reasonably fixed.

Simultaneously, as shown in Figure 3, the anchor net 17 material laying of step 1, first make the anchor net 17 material of suitable size, the anchor net 17 width is equal to the non-impact surface width, and the anchor net 17 begins to surround the rock from the drilling rock surface. Then the material of the anchor rod 14 is passed through the anchor net 17 and the rock mass test piece 16, and the tray 11, the dynamic pressure sensor 13 and the lock 12 are installed at both ends in order to form the anchor net coupling to support the rock mass.

The material of the bolt 14 and the anchor net 17 for supporting the rock mass by the coupling of the anchor net is made of an ideal elastic-plastic material, which has the characteristics of high prestress, high constant resistance, high energy absorption, and high elongation. Anchor materials include NPR (Negative Poisson Ratio) materials, TWIP (Twinning Induced Plasticity Steel) high-strength and high-toughness materials and other ideal plastic materials.

It should be pointed out that the pre-tightening force of the anchor rod 14 on the test piece can be adjusted, and different pre-tightening forces are configured for different samples to obtain impact test data respectively, and the impact resistance of the samples under different pre-tightening forces are compared and analyzed; similarly, For the anchor rod 14 and the anchor net 17, different samples can be configured with anchoring materials of different length specifications and different diameter specifications, and can also be configured as different materials. Similarly, the test data are respectively obtained for the anchoring materials under different configurations. The impact resistance of samples under different configurations was compared and analyzed.

In addition, the drilling parameters on the rock mass test piece 16 can also be adjusted, and different samples are configured with different numbers, different spacing, different layouts, and different apertures of drilling holes, and the impact test data are obtained separately to analyze the different drilling holes. Configure the impact resistance of the sample.

As shown in Figure 1 and Figure 2, the monitoring components include pressure monitoring components, stress and strain monitoring components, displacement monitoring components and high-speed camera systems. The pressure monitoring element is composed of a dynamic pressure sensor 13 and a charge amplifier, and the stress and strain monitoring element is composed of a strain gauge 10 and a dynamic strain acquisition instrument. The displacement monitoring element is composed of a laser extensometer 9, which is perpendicular to the impact direction and placed on one side of the coupling specimen 7 to monitor the displacement of the rock mass specimen 16, the anchor net 17 and the anchor rod 14.

The pressure monitoring element is arranged on the anchor rod 14 , the stress and strain monitoring element is arranged on the coupling test piece 7 , and the image acquisition element acquires images during the impact test, and the image acquisition element can be a high-speed camera 6 .

As shown in FIG. 1 , the strain distribution on the surface of the coupling specimen 7 is calculated.

The digital image correlation method is used to calculate the correlation of the speckle image gray level before and after the surface deformation of the specimen, so as to obtain the displacement and strain parameters of the specimen. First, calculate the correlation coefficient between all points on the deformed image within a certain range and the reference point of the image before deformation, and then use the point with the largest correlation coefficient as the target point. On this basis, the displacement before and after deformation can be obtained by calculating the coordinate difference between the reference point and the target point, and then the strain of the rock mass can be calculated.

As shown in Fig. 1, calculate the fractal dimension of the crack on the surface of coupling specimen 7.

The fractal dimension characterizes the irregularity and complexity of the crack pattern. The fractal dimension of rock mass cracks is measured by the box dimension method. Square grids (a*a) with different yardages are used to cover the measured area. The grid size required to cover the image can be calculated for a given grid size. number, and fit it.

In the formula, a is the yardstick of the grid, N(a) is the corresponding grid number, D is the box dimension, and A is the corresponding coefficient.

As shown in Fig. 1, the failure strength of coupling specimen 7 is calculated.

The dynamic pressure sensor 13 is used to monitor the pressure versus time curve, and the peak point of the curve is defined as the failure strength of the rock mass.

As shown in FIG. 1 , the axial deformation of the anchor rod 14 is calculated.

The displacement of the anchor rod 14 is measured in real time by the laser extensometer 9, and the elongation of the anchor rod 14 is calculated.

As shown in Figure 1, calculate the energy absorption capacity improvement coefficient.

Obtain the change curve of the axial force F of the anchor rod 14 with time t through the dynamic pressure sensor 13, and obtain the change curve of the deformation x of the anchor rod 14 with time t through the laser extensometer 9, so as to obtain the axial force F = f ( x ) with displacement deformation The change curve of , and further obtain the energy ΔE _B absorbed by the anchor rod 14 during the impact process,

In the formula, ΔE _B is the impact energy absorbed by the anchor rod 14, S is the final displacement of the anchor rod 14, f(x) is the axial force of the anchor rod 14, and x is the displacement deformation of the anchor rod 14.

According to the law of conservation of energy, we know that:

where ΔE _tot is the total absorbed energy of the coupling specimen 7, ΔE _B is the impact energy absorbed by the bolt 14, ΔE _R is the impact energy absorbed by the rock mass, ΔE _W is the impact energy absorbed by the anchor net 17, O(ΔE) is The trace energy dissipated in other forms such as heat energy and sound energy during the impact process, m is the mass of the bullet 2, and v is the initial velocity of the bullet.

The initial velocity of the bullet 2 is obtained by the laser velocimeter, and the impact energy ΔE _tot absorbed by the coupling specimen 7 is obtained through calculation combined with the mass of the rock mass.

Further calculation shows that the energy absorption rate η of the anchor rod 14 is the percentage of the ratio of the energy ΔE _B absorbed by the anchor rod 14 to the total absorbed energy ΔE _tot of the coupling specimen 7 .

By comparing the total absorbed energy ΔE _non of the unsupported rock mass under dynamic impact, the improvement coefficient α of the coupling energy absorption capacity of the anchor network 17 is established _. Percentage of energy ΔEnon ratio absorbed _by unsupported rock mass specimen:

As shown in Fig. 1, the debris distribution characteristics of coupling specimen 7 are calculated.

The debris after the coupling test piece 7 was destroyed was screened, and the particle size was divided into coarse-grained debris (particle size>30mm), medium-grained debris (5-30mm), fine-grained debris (0.075-5mm) and Particulate debris (<0.075mm) 4 grain groups. Weigh the mass of rock debris sieved out of each granule group, and calculate the ratio of the mass of each granule group to the total mass.

As shown in Figure 4, firstly, the six indicators of the coupling specimen 7 surface strain distribution, crack fractal dimension, rock mass failure strength, anchor rod 14 axial deformation, energy absorption capacity improvement coefficient, and rock mass debris distribution characteristics were analyzed. Standardized processing.

Secondly, the subjective and objective comprehensive weighting method of "analytic hierarchy process + entropy weight method" is used to obtain the weight of each index.

The practical experience of experts is introduced through the analytic hierarchy process, and the proportion w _aj of various indicators is determined. The anchoring effect of rock mass is taken as the target layer of hierarchical analysis, and excellent, good, qualified and unqualified are taken as the scheme layer, and the surface average strain, crack fractal dimension, rock mass failure strength, anchor rod 14 elongation, and energy absorption capacity are improved. The coefficient and the mass proportion of debris with different particle sizes are used as the criterion layer to construct a hierarchical structure model for rock mass anchorage effect evaluation.

In order to make up for the subjectivity of the AHP, the entropy weight method is used to determine the weight w _bj of various indicators. Combining the weight calculation results of the above two methods, the comprehensive weight of the index is proposed. The expression of the comprehensive weight w _j is:

In the formula: a —coefficient of weight w _aj ; b —coefficient of weight w _bj ; w _aj is weight obtained by AHP; w _bj is weight obtained by entropy weight method.

Finally, the fuzzy comprehensive evaluation method is used to evaluate the rock mass anchorage effect.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. The dynamic impact test and evaluation method of the anchor net coupled supporting rock mass is characterized by comprising the following steps:

arranging an anchor net and an anchor rod on a non-impact surface of the cubic rock mass test piece, pre-tightening, spraying speckles on the surface of the test piece, and obtaining a coupling test piece;

arranging a monitoring assembly on the coupling test piece, and applying a high-strain-rate impact load;

acquiring data of the coupling test piece under impact through the monitoring assembly, and collecting rock mass debris;

processing and analyzing the acquired data, and evaluating the anchoring effect according to the indexes;

wherein, the anchor effect index includes: the surface strain of the rock mass, the crack evolution characteristic, the rock mass destruction strength, the deformation of the anchor rod, the energy absorption capacity improvement coefficient and the rock mass debris distribution characteristic;

the anchor rods are arranged at four corners of the side surface of the test piece, the four corners of the side surface are respectively provided with the anchor rods penetrating through the test piece, and pre-tightening force is applied to the anchor rods after the anchor nets are arranged; the anchor net is continuously arranged around the non-impact surface of the test piece, wraps the test piece and avoids the anchor rod, and pressure monitoring elements are arranged at two ends of the anchor rod;

the evaluation comprises the following steps:

carrying out standardization treatment on each evaluation index;

calculating the weight of each index by adopting an subjective and objective comprehensive weighting method;

and evaluating the rock mass anchoring effect by using a fuzzy comprehensive evaluation method.

2. The dynamic impact test and evaluation method for the anchor net coupled and supported rock mass according to claim 1, wherein the pre-tightening force of the anchor rods on the test piece is adjustable, different pre-tightening forces are configured for different samples to respectively obtain impact test data, and the impact resistance of the samples under different pre-tightening forces is contrastively analyzed.

3. The dynamic impact test and evaluation method for the anchor net coupled supporting rock body according to claim 1, wherein the monitoring assembly comprises a pressure monitoring element, a stress-strain monitoring element, a displacement monitoring element and an image acquisition element; the pressure monitoring component is arranged in the stock, and the stress-strain monitoring component is arranged in the coupling test piece, and the displacement monitoring component is arranged in the coupling test piece side to monitoring rock mass, anchor net and stock displacement, image acquisition component obtain the image when impact test.

4. The method for testing and evaluating dynamic impact of an anchor net coupled supporting rock mass according to claim 1, characterized by performing correlation calculation on the speckle image gray levels before and after the surface of the coupling test piece is deformed to obtain the displacement and strain parameters of the test piece and calculate the strain distribution on the surface of the coupling test piece rock mass.

5. The dynamic impact test and evaluation method of the anchor net coupled timbering rock mass according to claim 1, characterized in that the measurement is performed by a box-dimension method, square lattices with different yardsticks are adopted to cover the measured area, the yardstick of the lattice is given and the number of the squares required for covering the image is calculated, fitting is performed to obtain the fractal dimension of the rock cracks, and the crack evolution characteristics are calculated.

6. The method for testing and evaluating the dynamic impact of the anchor net coupled support rock mass according to claim 1, characterized in that a curve of pressure variation with time is obtained by monitoring with a dynamic pressure sensor arranged on the anchor rod, and a peak point of the curve is defined as the destruction strength of the rock mass; and measuring the displacement of the anchor rod in real time by using a laser extensometer, and calculating the elongation of the anchor rod to obtain the deformation of the anchor rod.

7. The method for testing and evaluating dynamic impact of an anchor net coupled timbering rock mass according to claim 1, wherein the energy absorbed by the coupled test piece and the energy absorbed by the non-timbering rock mass test piece are calculated respectively, and the energy absorption capacity improvement coefficient is equal to the ratio of the total energy absorbed by the coupled test piece to the total energy absorbed by the non-timbering rock mass test piece;

and screening the fragments of the damaged anchor net coupling support rock mass according to the particle size to obtain multiple groups of fragments with different particle sizes, and calculating the ratio of the mass of each group of fragments to the total mass.

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